1. Field of the Invention
The invention relates to a photo-semiconductor module and a method for manufacturing the same.
2. Description of the Related Art
The optical fiber features xe2x80x9csmall lossxe2x80x9d, xe2x80x9csmall diameterxe2x80x9d, and xe2x80x9clight weightxe2x80x9d to thereby reduce the loss significantly as compared to a conventional metallic cable. This difference is remarkable in high speed transmission of signals. To provide broadband services to the general homes in the near future, it is indispensable to develop a low-cost, high-band, and high-sensitivity light reception terminal (ONU: Optical Network Unit).
In realization of a low-cost, high-band, and high-sensitivity light reception terminal (ONU), a super-lattice avalanche photo-diode (hereinafter abbreviated as APD) and a Pin-photodiode (hereinafter abbreviated as PinPD) are drawing the attention from the industries as a photo-receptor element. These photo-receptor elements have been desired to be further improved in characteristics (especially high-frequency characteristic).
In view of the above, it is a main object of the invention to improve the high-frequency characteristic of a light-receiving photo-semiconductor device.
To achieve this object, in short, a photo-semiconductor module of the invention comprises a circuit board, a light-receiving photo-semiconductor device which is flip-chip-wise mounted on this circuit board, and an optical fiber which is fixed to the mounting face or its back face of the light-receiving photo-semiconductor device.
This configuration of the invention makes it possible to connect a light-receiving photo-semiconductor device to the circuit board with a short wiring distance, thus improving the high-frequency characteristic.
Also, the flip-chip-wise mounting method makes it possible to directly radiate heat from the back face of the light-receiving photo-semiconductor device, thus improving the hear radiation performance as compared to a conventional packaging method (by use of a resin-molded product).
Further, by the invention, an optical fiber can be slid on the mounting face or its back face of the light-receiving photo-semiconductor device so that it may be fixed at such a point thereon so as to give the largest light receiving sensitivity, in order to enable alignment while preserving sufficient output properties, thus reducing the manufacturing costs. In particular, the back face of a light-receiving photo-semiconductor device is mirror-face finished often, thus having good flatness originally. This feature facilitates alignment and fixing of an optical fiber onto the back face of the device, thus further improving the productivity.
To align an optical fiber to a light-receiving photo-semiconductor device, the optical fiber may expectedly slid in an alignment groove formed in the surface of the circuit board. By such a method, however, the groove must be machined at a high precision level and also be aligned with the light-receiving photo-semiconductor device at a high accuracy, thus contributing to an increase in the manufacturing costs. Such problems can be solved by the invention.
By the invention, the light-receiving photo-semiconductor device has a photo-absorbing layer formed therein, so that preferably the optical fiber is fixed as opposed to this photo-absorbing layer in a direction perpendicular to the mounting surface. Such a configuration improves the photo-absorbing efficiency.
By the invention, the circuit board has a connection electrode, so that preferably the input/output terminal electrodes of the light-receiving photo-semiconductor device are connected to this connection electrode via a protruding electrode and a conductive adhesive agent.
Also, by the invention, the circuit board has a connection electrode, so that preferably the input/output terminal electrodes of the light-receiving photo-semiconductor device are connected to this connection electrode via solder.
Such a configuration makes it possible to securely connect the device to the circuit board with a short wiring distance, thus further improving the high-frequency characteristic.
By the invention, preferably the surroundings of a connection between the input/output terminal electrodes and the connection electrode are encapsulated with an encapsulating resin. By doing so, a simple construction of resin encapsulation is enough to encapsulate the photo-semiconductor module, thus reducing the costs by that much.
In this case, to secure encapsulation, preferably the opposing portion between the light-receiving photo-semiconductor device and the circuit board except the connection between the input/output terminal electrodes and the connection electrode is encapsulated with the encapsulating resin.
By the invention, the back face is provided with a mounting hole toward the mounting face so that the optical fiber may preferably be inserted into it and fixed. This configuration facilitates and ensures the fixation of the optical fiber.
By the invention, preferably the mounting hole has such a depth that extends to a vicinity of the photo-absorbing layer of the light-receiving photo-semiconductor device. Thus, the photo-absorbing efficiency can be improved further.
By the invention, preferably the light-receiving photo-semiconductor device employs a compound semiconductor substrate having a Pin-photodiode. By thus using the Pin-photodiode, it is possible to obtain a photo-semiconductor module stable in characteristics and reliabilities.
In this case, the circuit board has a connection electrode, so that preferably the connection electrode connected to either one of the P-side electrode and the N-side electrode of the Pin-photodiode is provided at such a site on the circuit board that is opposed to a periphery of the light-receiving photo-semiconductor device. Such a configuration suppresses the occurrence of a floating capacitance between the connection electrode of the circuit board and the light-receiving photo-semiconductor device, thus further improving the high-frequency characteristic.
By the invention, an auxiliary mounting plate with a through-hole is further comprised, so that preferably the auxiliary mounting plate is fixed to the back face with the optical fiber as inserted and fixed to the through-hole to thereby fix the optical fiber to the light-receiving photo-semiconductor device, thus facilitating and securing the fixation of the optical fiber.
In this case, preferably an encapsulating resin is comprised to encapsulate the surroundings of a connection between the input/output terminal electrodes and the connection electrode to thereby fix the auxiliary mounting plate to the back face with this encapsulating resin, thus further facilitating and securing the fixation of the optical fiber.
A photo-semiconductor module of the invention can be manufactured by a method comprising the steps of: forming a protruding electrode on the input/output terminal electrode provided on the mounting face to then give a conductive adhesive agent to this protruding electrode; installing the light-receiving photo-semiconductor device to the circuit board in such a manner that the input/output terminal electrode may butt against the connection electrode provided on the circuit board; hardening the conductive adhesive agent to mount the light-receiving photo-semiconductor device to the circuit board; encapsulating a connection site between the light-receiving photo-semiconductor device and the circuit board with an encapsulating resin; and fixing an optical fiber to the back face.
Similarly, a photo-semiconductor module of the invention can be manufactured by a method comprising the steps of: supplying solder to a connection electrode provided on the circuit board; installing the light-receiving photo-semiconductor device to the circuit board in such a manner that the input/output terminal electrode provided on the mounting face may butt against the connection electrode; melting the solder to mount the light-receiving photo-semiconductor device to the circuit board, encapsulating a connection site between the light-receiving photo-semiconductor device and the circuit board with an encapsulating resin; and fixing an optical fiber to the back face.
In this case, preferably a photo-hardening resin is used as the optical-fiber fixing adhesive agent and the encapsulating resin to thereby photo-harden both these encapsulating resin and optical-fiber fixing resin simultaneously, thus simplifying the step of hardening these resins.
Also, to use a compound semiconductor substrate having a Pin-photodiode to make the light-receiving photo-semiconductor device thereon, preferably the protruding electrode is formed on the terminal electrode with both the shorter-side faces of the compound semiconductor substrate as sandwiched by a jig to thereby enable avoiding damaging of the light-receiving photo-semiconductor device made of even such a relatively brittle substance as a compound semiconductor substrate.
Also, to mount a light-receiving photo-semiconductor device to the circuit board using solder, preferably heat and load are inflicted on the solder to thereby produce a diffused compound between the solder and the input/output terminal electrode, thus enabling securely interconnecting the connection electrode and the input/output terminal electrode without performing an extra step of applying flux to the solder.